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208 lines
9.3 KiB
C#
208 lines
9.3 KiB
C#
// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
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// See the LICENCE file in the repository root for full licence text.
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using System;
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using System.Collections.Generic;
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using System.Linq;
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using System.Threading;
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namespace osu.Game.Rulesets.Objects
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{
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public static class SliderEventGenerator
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{
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/// <summary>
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/// Historically, slider's final tick (aka the place where the slider would receive a final judgement) was offset by -36 ms. Originally this was
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/// done to workaround a technical detail (unimportant), but over the years it has become an expectation of players that you don't need to hold
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/// until the true end of the slider. This very small amount of leniency makes it easier to jump away from fast sliders to the next hit object.
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///
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/// After discussion on how this should be handled going forward, players have unanimously stated that this lenience should remain in some way.
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/// These days, this is implemented in the drawable implementation of Slider in the osu! ruleset.
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///
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/// We need to keep the <see cref="SliderEventType.LegacyLastTick"/> *only* for osu!catch conversion, which relies on it to generate tiny ticks
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/// correctly.
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/// </summary>
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public const double TAIL_LENIENCY = -36;
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public static IEnumerable<SliderEventDescriptor> Generate(double startTime, double spanDuration, double velocity, double tickDistance, double totalDistance, int spanCount,
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CancellationToken cancellationToken = default)
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{
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// A very lenient maximum length of a slider for ticks to be generated.
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// This exists for edge cases such as /b/1573664 where the beatmap has been edited by the user, and should never be reached in normal usage.
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const double max_length = 100000;
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double length = Math.Min(max_length, totalDistance);
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tickDistance = Math.Clamp(tickDistance, 0, length);
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double minDistanceFromEnd = velocity * 10;
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yield return new SliderEventDescriptor
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{
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Type = SliderEventType.Head,
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SpanIndex = 0,
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SpanStartTime = startTime,
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Time = startTime,
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PathProgress = 0,
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};
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if (tickDistance != 0)
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{
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for (int span = 0; span < spanCount; span++)
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{
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double spanStartTime = startTime + span * spanDuration;
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bool reversed = span % 2 == 1;
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var ticks = generateTicks(span, spanStartTime, spanDuration, reversed, length, tickDistance, minDistanceFromEnd, cancellationToken);
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if (reversed)
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{
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// For repeat spans, ticks are returned in reverse-StartTime order, which is undesirable for some rulesets
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ticks = ticks.Reverse();
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}
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foreach (var e in ticks)
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yield return e;
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if (span < spanCount - 1)
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{
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yield return new SliderEventDescriptor
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{
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Type = SliderEventType.Repeat,
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SpanIndex = span,
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SpanStartTime = startTime + span * spanDuration,
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Time = spanStartTime + spanDuration,
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PathProgress = (span + 1) % 2,
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};
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}
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}
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}
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double totalDuration = spanCount * spanDuration;
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// Okay, I'll level with you. I made a mistake. It was 2007.
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// Times were simpler. osu! was but in its infancy and sliders were a new concept.
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// A hack was made, which has unfortunately lived through until this day.
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//
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// This legacy tick is used for some calculations and judgements where audio output is not required.
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// Generally we are keeping this around just for difficulty compatibility.
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// Optimistically we do not want to ever use this for anything user-facing going forwards.
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int finalSpanIndex = spanCount - 1;
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double finalSpanStartTime = startTime + finalSpanIndex * spanDuration;
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// Note that `finalSpanStartTime + spanDuration ≈ startTime + totalDuration`, but we write it like this to match floating point precision
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// of stable.
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//
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// So thinking about this in a saner way, the time of the LegacyLastTick is
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//
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// `slider.StartTime + max(slider.Duration / 2, slider.Duration - 36)`
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//
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// As a slider gets shorter than 72 ms, the leniency offered falls below the 36 ms `TAIL_LENIENCY` constant.
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double legacyLastTickTime = Math.Max(startTime + totalDuration / 2, (finalSpanStartTime + spanDuration) + TAIL_LENIENCY);
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double legacyLastTickProgress = (legacyLastTickTime - finalSpanStartTime) / spanDuration;
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if (spanCount % 2 == 0) legacyLastTickProgress = 1 - legacyLastTickProgress;
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yield return new SliderEventDescriptor
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{
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Type = SliderEventType.LegacyLastTick,
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SpanIndex = finalSpanIndex,
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SpanStartTime = finalSpanStartTime,
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Time = legacyLastTickTime,
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PathProgress = legacyLastTickProgress,
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};
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yield return new SliderEventDescriptor
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{
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Type = SliderEventType.Tail,
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SpanIndex = finalSpanIndex,
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SpanStartTime = startTime + (spanCount - 1) * spanDuration,
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Time = startTime + totalDuration,
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PathProgress = spanCount % 2,
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};
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}
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/// <summary>
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/// Generates the ticks for a span of the slider.
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/// </summary>
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/// <param name="spanIndex">The span index.</param>
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/// <param name="spanStartTime">The start time of the span.</param>
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/// <param name="spanDuration">The duration of the span.</param>
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/// <param name="reversed">Whether the span is reversed.</param>
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/// <param name="length">The length of the path.</param>
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/// <param name="tickDistance">The distance between each tick.</param>
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/// <param name="minDistanceFromEnd">The distance from the end of the path at which ticks are not allowed to be added.</param>
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/// <param name="cancellationToken">The cancellation token.</param>
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/// <returns>A <see cref="SliderEventDescriptor"/> for each tick. If <paramref name="reversed"/> is true, the ticks will be returned in reverse-StartTime order.</returns>
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private static IEnumerable<SliderEventDescriptor> generateTicks(int spanIndex, double spanStartTime, double spanDuration, bool reversed, double length, double tickDistance,
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double minDistanceFromEnd, CancellationToken cancellationToken = default)
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{
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for (double d = tickDistance; d <= length; d += tickDistance)
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{
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cancellationToken.ThrowIfCancellationRequested();
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if (d >= length - minDistanceFromEnd)
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break;
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// Always generate ticks from the start of the path rather than the span to ensure that ticks in repeat spans are positioned identically to those in non-repeat spans
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double pathProgress = d / length;
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double timeProgress = reversed ? 1 - pathProgress : pathProgress;
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yield return new SliderEventDescriptor
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{
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Type = SliderEventType.Tick,
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SpanIndex = spanIndex,
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SpanStartTime = spanStartTime,
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Time = spanStartTime + timeProgress * spanDuration,
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PathProgress = pathProgress,
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};
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}
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}
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}
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/// <summary>
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/// Describes a point in time on a slider given special meaning.
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/// Should be used by rulesets to visualise the slider.
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/// </summary>
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public struct SliderEventDescriptor
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{
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/// <summary>
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/// The type of event.
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/// </summary>
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public SliderEventType Type;
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/// <summary>
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/// The time of this event.
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/// </summary>
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public double Time;
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/// <summary>
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/// The zero-based index of the span. In the case of repeat sliders, this will increase after each <see cref="SliderEventType.Repeat"/>.
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/// </summary>
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public int SpanIndex;
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/// <summary>
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/// The time at which the contained <see cref="SpanIndex"/> begins.
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/// </summary>
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public double SpanStartTime;
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/// <summary>
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/// The progress along the slider's <see cref="SliderPath"/> at which this event occurs.
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/// </summary>
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public double PathProgress;
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}
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public enum SliderEventType
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{
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Tick,
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/// <summary>
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/// Occurs just before the tail. See <see cref="SliderEventGenerator.TAIL_LENIENCY"/>.
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/// Should generally be ignored.
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/// </summary>
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LegacyLastTick,
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Head,
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Tail,
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Repeat
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}
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}
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